Effects of cattle manure addition on soil organic carbon mineralization and priming effects under long-term fertilization regimes

Abstract: The mineralization of soil organic carbon (SOC) is an important part of carbon cycle in the terrestrial ecosystem, and it is directly related to the nutrient cycling and utilization in the soil, crop productivity, greenhouse gases emission, and SOC storage and so on. It is reported that the SOC mineralization is significantly affected by the environmental factors such as different fertilization practices, the exogenous organic matter addition and so on, and even small changes of it can lead to higher impact on the dynamics of soil ecosystems. In order to reveal the responses of cattle manure addition on the mineralization and the priming effects under long-term fertilization regimes, an incubation experiment was conducted to investigate the effects of equal rate of cattle manure addition on the mineralization of SOC and contents of soil labile organic carbon fractions (microbial biomass carbon, MBC; dissolved organic carbon, DOC; particulate organic carbon, POC; and easily oxidizable carbon, EOC) in the long-term fertilizer trial (control of no-fertilizer, CK; standard rate of organic manure treatment, SMA; standard rate of mineral fertilizer treatment, SMF; half-standard rate of organic manure plus half-standard rate of mineral fertilizer treatment,1/2(SMA+SMF)), which were established in 1986 in Yucheng site, Shandong province, China. During incubation, soil moisture was adjusted to 60% of the field capacity with deionized water, and the fresh soil sample (equal to 100 g dry soil), adding cattle manure or not, was placed into a 500 mL wide-mouthed bottle that sealed with a rubber plug and was incubated in the dark for 79 d. The bottle plug was opened for gas exchange at regular intervals, and the soil moisture was adjusted gravimetrically with deionized water to maintain 60% field capacity. We determined soil chemical properties and labile organic carbon fractions using standard methods and the SOC mineralization by collecting gas at regular intervals in a 79 d incubation experiment. Additionally, we investigated the relationships between priming effects of soil organic carbon mineralization among different fertilized soils with cattle manure addition and soil nutrients with redundancy analysis (RDA). The results showed that the curve of accumulative mineralization amounts of SOC in the different fertilizer-treated soils were fitting with first-order kinetical equation, and the SOC mineralization rate constants in CK, SMF and 1/2(SMA+SMF) with cattle manure addition increased 21.74%, 35.00% and 45.00%, respectively; and the positive priming effects in CK and SMF treatments with cattle manure addition were 48.56% and 48.43%, much higher than those in the SMA and 1/2(SMA+SMF) treatments. Moreover, cattle manure addition significantly increased the contents of SOC, MBC, POC and EOC, but significantly reduced DOC content. Redundancy analysis showed that the priming effects of SOC mineralization in long-term fertilized soils with cattle manure addition had significantly positive correlations with the ratios of soil organic carbon and nitrogen fractions contents, but had significantly negative correlations with the soil nutrient contents (SOC; total nitrogen; available phosphorus, available potassium). In conclusion, this study is beneficial to achieving the maximum benefits of agricultural resources and applying organic fertilizer reasonably, which provides a theoretical basis for sustainable development of farmland ecosystem.